public class MySingleList implements SingleLinkedList{
    static class ListNode{
       public int val;
       public ListNode next;

       public ListNode(int val) {
        this.val = val;
    }
}


public ListNode head;
    @Override
    public void addFirst(int data) {

    }

    @Override
    public void addLast(int data) {

    }

    @Override
    public void addIndex(int index, int data) {

    }

    @Override
    public boolean contains(int key) {
        return false;
    }

    @Override
    public void remove(int key) {

    }

    @Override
    public void removeAllKey(int key) {

    }

    @Override
    public int size() {
        return 0;
    }

    @Override
    public void clear() {

    }

    @Override
    public void display() {
        while (head != );

    }
}
